discouraged

Every month since March I test and continue to get a heartbreaking negative results. I already have 3 children and my husband has 3 of his own so we know it's not any issues with either of us, but why can't we get pregnant. I turned 30 last December so I know I'm still at the right age. In the past, when I became pregnant with all three of my kids it was an accidental, few times of unprotected sex and immediately became pregnant. Now that I am trying and want it so badly it seems impossible to ever get that positive line my husband and I are wanting so badly. How long did it take everyone else to conceive and how to you continue handling the negative test results each month? Is there something more I should be doing to make my chances higher?